Have you tried adjusting the input level to your microphone? I had to fiddle with mine a little to get consistent results for all commands.

Go into settings and then type "sound" in the search box. Click "sound settings". About 1/2 way down, click "Device properties and test microphone". Click the "Test" button at the bottom.

Speak "select command a" just like you have been, and see if the little sound meter bar under the level control is too weak (stays within the 1st 10-15mm on the left) or too strong (slams all the way to the right) when you speak. Try to get it to where every syllable of the entire phrase moves the bar at least 1/2 way (closer to 3/4 is preferable).

I left that window open and whenever FS2Crew wouldn't recognize a command during a flight, I'd alt tab to it and move that volume slider 1 click and speak the command again (I had to "range" it a little at first to figure out which direction it was off - try a few clicks lower, then a few higher). You can position the window over P3D so that you can watch the green bar at the same time. If you click on the volume slider, you can use the left and right arrows on your keyboard while you keep adjusting, repeating the command, and watching the green bar. After a few flights, I dialed in 89 as the correct level for mine, and now FS2Crew gets it right almost all the time. 

I tried using Voice Commands for the first time in a couple years tonight and it would not let me run the descent checklist. Whenever I would call for it, the speech recognition would think I'm saying "off schedule descent checklist" and do nothing, regardless of if my diction was clear or not.

Hi Raymond,

With an American accent, your speech recognition results should generally be extremely good.

Make sure you ran the voice training and cross check the manual for the expected phrases.